Current limiting interruption of currents at high voltages

ABSTRACT

An improved circuit for the current limiting interruption of alternating or direct currents in a power main at high voltages of the type wherein an energy absorbing circuit and a capacitor are each connected in parallel with a circuit path including a commutation or interrupter switch so that upon opening of the switch the current flowing therein will be commutated into the parallelly connected circuits wherein the current will be reduced to a residual value which is switched off by a subsequently connected circuit breaker. A further commutating switch is connected in series with the first mentioned commutation switch and an ohmic resistance connected in parallel therewith so that the total series resistance of the ohmic resistance and the arc resistance of the first mentioned commutation switch will be sufficient to cause the commutation of the main current into the energy absorbing and capacitor circuits.

United States Patent 1191 Salge et al. I

[54] CURRENT LIMITING INTERRUPTION OF CURRENTS AT HIGH VOLTAGESInventors: Jurgen Salge, Salzgitter-Osterlinde; Hagen Hartel,Braunschweig, both of Germany [73] Assignee: Dieter Kind, Braunschweig,Germany Filed: Aug. 5, 1971 Appl. No.: 169,362

Foreign Application Priority Data Aug. 6, 1970 Germany ..P 20 39 065.2

[56] References Cited UNITED STATES PATENTS 3,522,472 8/1970 Breitholtz.1 ..317/11 E 3,430,0 2 2/1969 Roth ....317 11 E 3,544,843 12 1970Sletten et a1 .317 11 A 1 1 June 5, 1973 5/1966 Stromet al. ..3l7/11A 81970 Willard ..317/11E Primary Examiner-James D. TrammellAttorney-George H. Spencer and Harvey Kaye [57] ABSTRACT parallel with acircuit path including a commutation or.

interrupter switch so that upon opening of the switch the currentflowing therein will be commutated into the parallelly connectedcircuitswherein the current will be reduced to a residual value which isswitched off by a subsequently connected circuit breaker. A furthercommutating switch is connected in series with the first mentionedcommutation switch and an ohmic resistance connected in paralleltherewith so that the total series resistance of the ohmic resistanceand the arc resistance of the first mentioned commutation switch will besufficient to cause the commutation of the main current into the energyabsorbing and capacitor circuits.

12 Claims, 5 Drawing Figures S R/ HS/ CURRENT LIMITING INTERRUPTION OFCURRENTS AT HIGH VOLTAGES BACKGROUND OF THE INVENTION The presentinvention relates to an improved method and apparatus for the currentlimiting interruption of direct and alternating currents at highvoltages. More particularly, the present invention relates to a method,and apparatus for this purpose in which the current to be switched offis forced to commutate via switching elements (commutation switches)into auxiliary paths having a high resistance which are connected inparallel with the commutation switch, so that the current is reduced toa residual value which is then switched off by a subsequently connectedcircuit breaker.

With a current-limiting switch-off in direct current as well asalternating current mains, the switching device must produce a switchvoltage after actuation which is greater than the driving voltage in thecircuit and it must absorb the energy furnished by the mains (includingthe energy stored in the inductances of mains) during the switchingprocess. These two requirements can be met up to certain current limitsby switches having intensive cooling of the generated are.

As is known, a switch can also be greatly relieved if auxiliary paths orby-passes are used for the voltage generation and for the energyconversion. This is done, for example, by connecting a capacitor and anenergy absorber in parallel with the commutation switch. However, theactual problem involved is the commutation of the current from theswitch into the parallel circuits. Although such a commutation can beobtained in principle with a sufficiently large parallel capacitance,the costs involved for the capacitors are high and accordingly often noteconomically justifiable. A current interrupting arrangement such asillustrated in FIG. 1 was for example proposed by D. Kind, E. Marx, K.Mollenhoff, J. Salge in the paper: Circuit-Breaker forHVDC-Transmissions, CIGRE 1968, Report No. 13-08.

This method for the current limiting interruption of a current at a highvoltage is shown schematically in FIG. 1, wherein L indicates theinductance of the mains or conductor, S is a commutation switch, forinstance a circuit-breaker with intensive cooling of the arc and S is aresidual current switch or circuit breaker. An auxiliary commutationcircuit including the series connection of an auxiliary switch HSresponsive to the arc voltage V,, of switch S, a capacitor C and aleakage inductance L,, and an absorber circuit A containing an energyabsorbing element such as an ohmic resistor R, a voltage dependentresistor R(i) or an inductance L are each connected in parallel with thecommutation switch S. The mains voltage V causes a current i to flowthrough this total circuit which current initially flows only as theswitch current i, through the commutation switch S and residual currentswitch S When switch S is open an arc voltage V,,(!) which increaseswith time is produced across switch S. When the value V, (t,,) V,, hasbeen reached, the auxiliary switch HS closes and effectively switchesthe circuit formed by the series resents the arc resistance of thecommutating switch S,

which increases with time t and which, within certain limits, alsoincreases its resistance even with decreasing current. During thecommutation process the current i is approximately constant, i.e., 1,. Atransfer of current from R into the parallel circuits can occur onlywhen R; can increase its resistance rapidly enough and when its valueapproaches infinity. This requirement can be made for a given circuitelement in that the duration of the commutation process is adapted tothe increase in resistance of the are produced by switch S. Thisincrease in the duration of the commutation process can be achieved, forexample, by the selection of a sufficiently large capacitance C.However, with the presently known commutation switches this leads tolarge banks of capacitors C which as indicated above leads to largeexpenditures.

SUMMARY OF THE INVENTION The above drawbacks of the prior artarrangements are avoided and a substantial improvement in thecommutation and thus a significant reduction in size of the requiredcapacitors is achieved, according to the present invention, by initiallytemporarily commutating the current to be switched off into an ohmicresistance connected in series with a switching path (commutatingswitch) and only thereafter commutating the current from this seriespath into a parallel circuit having an energy absorber so as to reducethe current to be interrupted to a residual value which is then switchedoff by a circuit breaker subsequently connected in the current main.

A number of embodiments of circuit arrangements according to theinvention are disclosed. According to one embodiment of the invention, apair of commutating or interrupter switches are connected in series inthe main and a highly resistive energy absorbing circuit is connected inparallel with this series connected of commutation switches. A circuit,including an ohmic resistor in series with an auxiliary switchresponsive to the arc voltage of a first of the pair of commutatingswitches, is connected in parallel with the first commuv tating switchand thus in series with the other of the pair of commutating switches.If required, a further auxiliary commutation circuit, including theseries connection of a capacitor, a leakage inductance and an auxiliaryswitch responsive to the are voltage of the other of said pair ofcommutation switches may be connected in parallel with the seriesconnection of the pair of commutating switches.

According to a preferred feature of the invention the ohmic resistorconnected in parallel with the first commutating switch is a wire whichexplodes at a desired current value, i.e., acts as a fuse.

According to a further embodiment of the invention, in order to providecurrent limiting interruption of cur rents of different values, aplurality of commutating switches, each having an ohmic resistor, i.e.,an exploding wire, dimensioned for the commutation of a differentcurrent value, connected in parallel therewith are connected in serieswith a further commutating switch, and the energy absorbing circuit, andif required the circuit containing the capacitor, are connected acrossthe series connection of all of the commutation switches.

According to still a further embodiment of the invention first andsecond commutating switches are connected in series in the main, theohmic resistor is connected in parallel with the first commutationswitch and a further circuit, including the series connection of acapacitor having a large capacitance but low rated voltage, a leakageinductance, and a unidirectional auxiliary switch responsive to the arcvoltage of the first commutation switch, is also connected in parallelwith the first commutation switch. The energy absorbing circuit and thecircuit including the capacitor and the auxiliary switch responsive tothe arc voltage of the second commutation switch, are each connected inparallel with the series connection of the two commutation switches.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic circuit diagramillustrating the principle of a circuit arrangement with commutationdevice according to the prior art.

FIG. 2 illustrates the equivalent circuit diagram for the arrangement ofFIG. 1 during the commutation process.

I FIG. 3 is a schematic circuit diagram of one embodiment of theinvention for the intermediate commutation of the current to be switchedoff into an exploding wire.

FIG. 4 is a schematic circuit diagram of a further embodiment of theinvention for the intermediate commutation of the current to be switchedoff into two seriesconnected exploding wires which are designed fordifferent currents.

FIG. 5 is a schematic circuit diagram of another embodiment of theinvention for the intermediate commutation of the current to be switchedoff into a current and/or time dependent resistor by means of anauxiliary commutation circuit.

DESCRIPTION OF THE PREFERRED EMBODIMENTS According to the presentinvention, the basic current circuits of the prior art are modified byproviding an additional circuit arrangement whereby, during thecommutation process an ohmic resistance is connected in series with thearc resistance R of the commutating switch so that the ohmic resistancetogether with the arc resistance permits commutation of the current tobe switched off from the commutation switch into the circuit containingthe capacitor and into the energy absorbing paths. As a result of thisadditional resistance, the total commutation arrangement need beequipped only with a small capacitor bank or even none at all.

Referring now to FIG. 3 there is shown a first embodiment of an improvedcommutation circuit according to the invention wherein, as in allsucceeding figures, the same reference numerals used in FIG. l areutilized to designate similar elements. According to this embodiment,two series connected commutation switches S, and S are connected in themain and the auxiliary circuits, i.e., the energy absorber A and thecircuit containing the capacitor C, auxiliary switch HS and the leakageinductance L,, are connected across the series connection of commutationswitches S, and S Connected in parallel with commutation switch S, is acircuit including the series connection of an auxiliary switch HS,,which is responsive to the arc voltage of switch 8,, and an ohmicresistance R,. Upon opening of switch 5,, and the subsequent closing ofauxiliary switch HS,, the current flowing in the main will flow throughthis resistance R, which provides a resistance value sufficiently highso that the series resistance of R,

and the arc resistance R of switch S, will cause commutation of the maincurrent into the auxiliary commutation circuits, i.e., the circuitcontaining the capacitor C and the energy absorber circuit A.Preferably, according to the present invention, the resistance R, isrealized by a wire which is dimensioned so that when a current of themagnitude flowing in the main is directed thereto, it will be heatedwithin a few milliseconds by the current and explode, i.e., act as afuse, thus causing a very high voltage. Thus, as a result of the highresistance R, produced by the explosion of the wire in conjunction withthe series-connected arc resistance R of switch 8,, it is possible toobtain dependable commuta tion of the current from commutating switch S,into the parallelly connected auxiliary commutation paths containing thecapacitor C and accordingly into the energy absorber A. Under certainconditions, it is even possible to do without the auxiliary commutationcircuit formed of auxiliary switch HS and capacitor C. Both of theswitches S, and S, are triggered at the same time by an opening command.The auxiliary switch HS, closes some milliseconds later. The moment oftriggering depends on the value of the arc voltage of the commutationswitch 8,. The auxiliary switch HS, closes some milliseconds after theclosing of the auxiliary switch HS, The moment of triggering for thisswitch depends on the value of the voltage of the series connection ofthe resistor R, and the switch 8,.

Since the wire providing the high resistance R, must be adapted to thecurrent value to be switched off for the commutation of the current fromthe switching path 8,, in order to switch off currents of differentvalues, a circuit according to FIG. 4 must be employed. According tothis embodiment of the invention, the commutating switch S, of FIG. 3 isrealized by the series connection of two switches S, and 8, each ofwhich has a series connection of an auxiliary switch HS,,, and HS,,, anda respective wire R, and R,,, connected in parallel therewith. Wire R,,is here designed for dependable commutation of the minimum occurringcurrent in the main and R,, is designed for commutation of the maximumoccurring current in the main. When switching the minimum current onlywire R,,, will explode, while when the maximum current is beingswitched, both wires will explode. Under these circumstances because ofthe dimensions of wire R,,,, for small currents the switching path S,will be triggered back. This, however, will have no influence on thefinal commutation from switch S into the auxiliary circuit. In order torealize a further optimization of the current commutation from switch S,into the wire, additional series connected switches S1". 5 S, etc., eachhaving a wire designed for a certain current value connected in paralleltherewith, may be provided. Since the wires must be replaced after eachswitching process, the arrangement corresponds to a type of fuse.

The three commutation switches S,,,, S,,,, S, are triggered at the sametime by an opening command. The auxiliary switches HS,,, and HS,,, closesome milliseconds later. The moment of triggering depends on the valueof the arc voltage of the commutation switches S,,, and S,,,. Theauxiliary switch HS, closes some milliseconds later. The moment oftriggering for this switch depends on the value of the voltage of theseries connection of the resistors R,,,, R and the commutation switch SV,,,(t) will be produced across switch S. When the value V ,(t,,) V hasbeen reached, auxiliary switch HS, will close and connect the capacitorC, in parallel with switch.S,'. As a result of the capacitance ofcapacitor C, being selected to be sufficiently large, commutation of themain current into the parallel path containing resistor R, is assured.Resistor R, is so designed that the voltage across it, after completionof the commutation, is relatively low so that capacitor C, need onlyhave a low rated voltage and thus only very low output. In thisembodiment the auxiliary switch HS, must be able to prevent currentfromflowing in the circuit containing capacitor C, after completion-of thecommutation of the current into resistor R,. Accordingly, auxiliaryswitch HS, may, for example, be a wiper switch, a spark path or gaphaving a series-connected diode, a triggered spark gap or path or athyristor. After commutation of the current into resistor R,, theresulting series connection of the resistance of resistor R, with thearc resistance R presents a total resistance which is much morefavorable for a commutation of the main current into the parallelcircuits including the capacitor C and the energy absorber A than if thecommutation into the same auxiliary circuits were to be effected only bythe arc resistance R of switch S The commutation is particularly favoredwhen R, increases with decreasing current or with increasing time. Bothof the switches S, and S are triggered at the' same time by openingcommand. The auxiliary switch HS, closes some milliseconds later. Thetriggering moment depends on the value of the arc voltage of thecommutation switch 8,. The auxiliary switch HS; closes some millisecondsafter the closing of the auxiliary switch 1-18,.

The disclosed circuit arrangements may also be used in seriesconnections so that the residual current can be reduced to any desiredlow value. It may also be advantageous to design the individual switches8,, S S,,,, S and possibly also further commutation switches as theterminals or partial arcs of a single switch.

It will be understood that the above description of the presentinvention is susceptible to various modifications, changes andadaptations, andthe same are intended to becomprehended within themeaning and range of equivalents of the appended claims.

We claim:

1. In a method for the current limiting interruption of direct andalternating currents flowing in a power main at high voltages in whichthe current to be switched off is forced to commutate via the opening ofa commutating switch into auxiliary parallelly connected circuit pathshaving a high resistance so that the current is reduced in the auxiliarypaths to a residual value which is switched off by a subsequentlyconnected circuit breaker, the improvement comprising temporarilycommutating the current flowing through said switch into a circuit pathincluding an ohmic resistor connected in series with said commutatingswitch (S prior to the commutation thereof into said parallellyconnected auxiliary circuit paths.

2. In a circuit arrangement for the current limiting interruption ofdirect and alternating currents flowing in a power main at high voltagehaving a first commutation switch which carries the current to beswitched off connected in a circuit path in series with the power mainand a highly resistive energy absorbing circuit, including a resistor oran inductance, connected in parallel with said circuit path, so that theopening of said first switch will cause the commutation of the currentto be switched off to said energy absorbing circuit wherein it isreduced to a residual value which is switched off by a circuit breakersubsequently connected in the power main, the improvement comprising: asecond commutation switch which also carries the current to be switchedoff connected in said circuit path in series with said first switch; andan ohmic resistance connected in series with said first commutationswitch and in parallel with said second commutation switch whereby uponopening of said second commutation switch, the current to be switchedoff is temporarily commutated through said resistance thereby connectingsame in series with the arc resistance of said first commutation switch.

3. The circuit arrangement defined in claim 2 including an auxiliaryswitch, which is responsive to the arc voltage across said secondcommutation switch, connected in series with said ohmic resistance.

4. The circuit arrangement defined in claim 2 including a furthercircuit connected in parallel with said circuit path, said furthercircuit including the series connection of an auxiliary switchresponsive to the arc voltage of said first commutation switch, a firstcapacitor, and a leakage inductance.

5. The circuit arrangement defined in claim 3 wherein said ohmicresistance is a wire which explodes upon being heated for a fewmilliseconds by a predetermined value of current passing therethrough.

6. The circuit arrangement defined in claim 4 including a furthercommutating switch connected in said circuit path in series with saidfirst and second commutation switches, and a further ohmic resistanceconnected in parallel with said further commutationswitch; each of saidohmic resistances being in the form of a wire which explodes upon beingheated for a few milliseconds by a predetermined value of currentpassing therethrough, with each of said wires being dimensioned toexplode for a different current value.

7. The circuit arrangement defined in claim 4 further including anadditional circuit means for aiding in the temporary commutation of thecurrent through said ohmic resistance; said additional circuit meansconsisting of the series connection of an auxiliary switch responsive tothe arc voltage of said second commutating switch, a further capacitorhaving a large capacitance but a low rated voltage compared to the mainsvoltage, and a leakage inductance, and being connected in parallel withsaid second commutating switch; said auxiliary switch being of the typewhich prevents a discharge of said further capacitor through the circuitpath formed by said first capacitor, said leakageinductance and saidfirst commutation switch upon completion of the commutation of thecurrent to said ohmic resistance.

subsequently connected diode, or a thyristor.

11. A circuit arrangement including a plurality of the circuitarrangements as defined in claim 2 connected in series so that theresidual current can be reduced to any desired low value.

12. The circuit arrangement defined in claim 2 wherein said commutatingswitches are terminals or partial arcs of a single switch.

1. In a method for the current limiting interruption of direct andalternating currents flowing in a power main at high voltages in whichthe current to be switched off is forced to commutate via the opening ofa commutating switch into auxiliary parallelly connected circuit pathshaving a high resistance so that the current is reduced in the auxiliarypaths to a residual value which is switched off by a subsequentlyconnected circuit breaker, the improvement comprising temporarilycommutating the current flowing through said switch into a circuit pathincluding an ohmic resistor connected in series with said commutatingswitch (S2) prior to the commutation thereof into said parallellyconnected auxiliary circuit paths.
 2. In a circuit arrangement for thecurrent limiting interruption of direct and alternating currents flowingin a power main at high voltage having a first commutation switch whichcarries the current to be switched off connected in a circuit path inseries with the poWer main and a highly resistive energy absorbingcircuit, including a resistor or an inductance, connected in parallelwith said circuit path, so that the opening of said first switch willcause the commutation of the current to be switched off to said energyabsorbing circuit wherein it is reduced to a residual value which isswitched off by a circuit breaker subsequently connected in the powermain, the improvement comprising: a second commutation switch which alsocarries the current to be switched off connected in said circuit path inseries with said first switch; and an ohmic resistance connected inseries with said first commutation switch and in parallel with saidsecond commutation switch whereby upon opening of said secondcommutation switch, the current to be switched off is temporarilycommutated through said resistance thereby connecting same in serieswith the arc resistance of said first commutation switch.
 3. The circuitarrangement defined in claim 2 including an auxiliary switch, which isresponsive to the arc voltage across said second commutation switch,connected in series with said ohmic resistance.
 4. The circuitarrangement defined in claim 2 including a further circuit connected inparallel with said circuit path, said further circuit including theseries connection of an auxiliary switch responsive to the arc voltageof said first commutation switch, a first capacitor, and a leakageinductance.
 5. The circuit arrangement defined in claim 3 wherein saidohmic resistance is a wire which explodes upon being heated for a fewmilliseconds by a predetermined value of current passing therethrough.6. The circuit arrangement defined in claim 4 including a furthercommutating switch connected in said circuit path in series with saidfirst and second commutation switches, and a further ohmic resistanceconnected in parallel with said further commutation switch; each of saidohmic resistances being in the form of a wire which explodes upon beingheated for a few milliseconds by a predetermined value of currentpassing therethrough, with each of said wires being dimensioned toexplode for a different current value.
 7. The circuit arrangementdefined in claim 4 further including an additional circuit means foraiding in the temporary commutation of the current through said ohmicresistance; said additional circuit means consisting of the seriesconnection of an auxiliary switch responsive to the arc voltage of saidsecond commutating switch, a further capacitor having a largecapacitance but a low rated voltage compared to the mains voltage, and aleakage inductance, and being connected in parallel with said secondcommutating switch; said auxiliary switch being of the type whichprevents a discharge of said further capacitor through the circuit pathformed by said first capacitor, said leakage inductance and said firstcommutation switch upon completion of the commutation of the current tosaid ohmic resistance.
 8. The circuit arrangement defined in claim 7wherein said ohmic resistance is a resistor having a constant value ofresistance.
 9. The circuit arrangement defined in claim 7 wherein saidohmic resistance is a resistor whose resistance value is currentdependent.
 10. The circuit arrangement defined in claim 7 wherein saidauxiliary switch is either a wiper switch, a triggered spark path, aswitch or a spark path with a subsequently connected diode, or athyristor.
 11. A circuit arrangement including a plurality of thecircuit arrangements as defined in claim 2 connected in series so thatthe residual current can be reduced to any desired low value.
 12. Thecircuit arrangement defined in claim 2 wherein said commutating switchesare terminals or partial arcs of a single switch.